Modeling is one of the most common tasks in the development of Information Systems (IS). Models such as ontologies, schemas, diagrams, patterns or architectures are used to build IS. Sometimes, the meaning of these terms and their differences are not clear so some are mixed up or bad used. The aim of this work is to clarify the concept of model through an analysis of the meaning of some common models used in IS. This proposal is presented by means of an ontology where we express our conceptualization of models according to two points of view: models as representations of a domain and models as reference frameworks.